Pushing Perishability

Sweet corn continues to be a valuable fresh-market crop for Florida growers. During the 2008-2009 season, Florida extended its reign as the No. 1-producing state, with a value exceeding $227 million harvested from 43,100 acres. Sweet corn is the second-ranked vegetable in the state, behind tomato, with an average season price of $16.28 per 42-pound crate. Supersweet varieties continue to dominate the fresh market and, although they remain sweet longer than traditional varieties after harvest, proper postharvest management is still critical to assure market quality and acceptability. There are principles and practices for keeping sweet corn quality fresh.

Quality And Perishability

High-quality corn is tender and sweet, and that begins with proper harvest maturity. Kernel juice should be milky for sugary (su1) and sugary enhanced (se) varieties, whereas shrunken 2 (sh2) varieties have watery juice. Ears should be picked when the tip kernels are filled but not oversized. Husks should be green and fresh in appearance with dried silks. Trimming flag leaves and shanks reduces moisture loss during handling and shipping; completely husked ears lose much less moisture than those with husks.

Sweet corn is one of the most perishable vegetables. Its high respiration and tendency to lose water mean that, if not cooled promptly and thoroughly after harvest, stored reserves in the kernel will be quickly consumed. This leads to loss of sweetness, shriveling (denting), tougher kernel texture, and dried husks. Corn that is cooled to near 32°F (0°C) within an hour or so of harvest can be expected to remain in good condition at that temperature for more than 14 days. However, failure to cool the ears properly shortens the postharvest life. For example, cooling to only 50°F (10°C) would shorten postharvest life by a factor of 4, or to less than four days.

Cooling Methods

Three methods effectively remove field heat. Hydrocooling is widely used because it can be applied to bulk corn in bins, to individual packages (returnable plastic containers-RPC’s; waxed cartons; wooden wirebound crates) and to pallets. Slush-ice cooling is a form of package icing, in which a slurry of finely crushed ice in water is injected into or on top of the packed corn container. Both hydrocooling and slush-ice cooling hydrate the corn. Vacuum cooling also is used to cool corn at high-volume operations; however, the corn must be wetted prior to cooling in order to minimize water loss.

Several factors decrease cooling efficiency, thus extending cooling time. The more the corn is packaged, the longer the cooling time because the package restricts contact between the cooling medium and the product. For example, crated corn requires 25% more cooling time than bulk-packed corn. Undersized cooling equipment is another common cause of delayed cooling, since the system does not have sufficient cooling capacity to maintain the setpoint water temperature.

Trimmed And Fresh-Cut

With increasing consumer demand for convenient, ready-to-eat vegetables, various types of husked and trimmed sweet corn, and even fresh-cut kernels, have been developed and marketed. These products are more perishable than traditional bulk sweet corn and, in order to remain fresh and appealing, they require special packaging to supplement temperature control and manage water loss and elevated respiration. If cut kernels are not handled exclusively at near 32°F or at slightly higher temperatures in modified atmosphere packaging, they can turn brown when cooked. Kernels removed intact from cobs don’t discolor when cooked, and they also maintain higher sugar content and better flavor than cut kernels.

Now is a good time to check over existing cooling systems prior to the start of the spring harvest season. Always work with a reputable refrigeration contractor with experience in fresh produce.

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